There have been proposed various processes for producing a pneumatic tire in which a green tire is formed on an outer circumferential surface of a rigid inner die made of metal, and in which the formed green tire is then placed inside a vulcanizing mold together with the rigid inner die and vulcanized (refer to Patent Documents 1 and 2, for example). According to the aforementioned production methods using the rigid inner die, a rubber-made bladder, which has been used heretofore, is no longer necessary. Thus, the step of removing the formed green tire from a making drum, or the like can be omitted. In addition, as compared with the case where the tire is produced using a bladder, the aforementioned production methods are advantageous in that the inner circumferential surface of the vulcanized tire can be accurately formed in a predetermined shape.
During the vulcanization, however, the green tire is only pressed by the vulcanizing mold from the outer side, so that the amount of pressing force acting on the inner circumferential surface of the green tire becomes small. Accordingly, for example, if the volumes of tire components are uneven in the inner circumferential surface of the tire, it is difficult to correct the unevenness, and an improvement in uniformity of the vulcanized tire is thus limited.
Moreover, when the inner circumferential surface of the green tire is pressed against the outer circumferential surface of the rigid inner die, a gap between split parts forming the rigid inner die leaves a mark on the inner circumferential surface of the vulcanized tire. This presents a problem of reduced quality of the external appearance.
In addition, butyl rubber is mainly used for an inner layer (innermost circumferential surface) of the green tire. Accordingly, an additional operation of, for example, applying a remover is required to separate the inner layer from the outer circumferential surface of the rigid inner die easily.
Moreover, the inner layer made of butyl rubber requires a certain degree of thickness to secure sufficient air permeation prevention performance. For this reason, such an inner layer is disadvantageous in reducing the weight of the tire. Accordingly, an inner layer which has excellent air permeation prevention performance and which is light in weight has been desired.    Patent Document 1: Japanese patent application Kokai publication No. 2001-88143    Patent Document 2: Japanese patent application Kokai publication No. 2003-340824